begin{tikzpicture}[cell/.style={rectangle,draw=black},
space/.style={minimum height=1.5em,matrix of nodes,row sep=-
pgflinewidth,column sep=-pgflinewidth,column 1/.style=
{font=ttfamily}},text depth=0.5ex,text height=2ex,nodes in empty cells]

matrix (matrice) [
space,
column 2/.style={minimum width=5em,nodes={cell,minimum width=3.5em}},
column 3/.style={nodes={cell,minimum width=4em}},
 column 4/.style={nodes={cell,minimum width=4em}}]
 {
 $t_1$   &6  & 6  & 7    \
 $t_2$   &3  & 3.5  & 8    \
 $t_3$   &4  & 9  & 9    \
 $t_4$   &7  & 9  & 0    \ };

 begin{axis}[left= of matrice,
 xlabel=time,
 ylabel=$f(textrm{temps})$,
 xtick distance=1,
 legend pos=north west
 ,grid=major]
 addplot  [color=green] table {
 Date GDP
 1 6
 2 3
 3 4
 4 7
 };
  addplot [color=blue] table {
 Date X
 1 5
 2 4
 3 5
 4 4
 };
 addplot [color=red]table {
Date X
1 5.2
2 4.2
3 5.1
4 4.05
 };
addplot [color=purple]table {
Date X
 1 3.2
 2 4.2
 3 5.19
 4 4.05
 };
 legend{$sensor 1$, $sensor 2$, $sensor2$}
 end{axis}
end{tikzpicture}